1. Field of the Invention
The present invention relates to a method for manufacturing (Li, Na, K)(Nb, Ta)O3 type piezoelectric material for use in an actuator and a sensor.
2. Description of the Related Art
A piezoelectric/electrostrictive actuator has an advantage in that displacement can precisely be controlled on the order of submicrons. Especially, in the piezoelectric/electrostrictive actuator in which a sintered body of a piezoelectric/electrostrictive porcelain composition is used as a piezoelectric/electrostrictive body, there are also other advantages in that the actuator has a high electromechanical change efficiency, a large generative force, a high responsivity, high durability and a small power consumption, and an actuator using these advantages is employed in a head of an ink jet printer, an injector of a diesel engine or the like.
As the piezoelectric/electrostrictive porcelain composition for the piezoelectric/electrostrictive actuator, heretofore, a Pb(Zr, Ti)O3 (PZT)-type piezoelectric/electrostrictive porcelain composition has been used, but there has been a strong fear of an influence of solute of lead from the sintered body on global environments, and hence a (Li, Na, K)(Nb, Ta)O3 type piezoelectric/electrostrictive porcelain composition has been investigated.
The (Li, Na, K)(Nb, Ta)O3 type piezoelectric material is usually sintered in the air or in an oxygen atmosphere at 1020 to 1250° C. for 0.15 to 4 hours (for example, Non-Patent Documents 1 to 3). The heating rate to reach the firing temperature is 200° C./h or 300° C./h, and the temperature rises at a constant heating rate from room temperature to the firing temperature (for example, Patent Document 1). There is also a research example in which the temperature is kept in a range of 600 to 650° C. for 1 to 5 hours in the heating process, whereby an organic binder added to improve formability of powder is removed (a de-binder process) (for example, Patent Document 1).
[Non-Patent Document 1] M. Matsubara et. al., Jpn. J. Appl. Phys. 44 (2005) pp. 6136-6142;
[Non-Patent Document 2] E. Hollenstein et. al., Appl. Phys. Lett. 87 (2005) 182905;
[Non-Patent Document 3] Y. Guo et. al., App. Phys. Lett. 85 (2004) 4121; and
[Patent Document 1] JP-A-2006-28001.
However, in the above prior art, the firing temperature and the de-binder are investigated, but the holding process at a temperature close to the firing temperature and the heating rate are not disclosed.
Moreover, the above prior art have the following problems.
(1) There are a large number of pores (grain boundaries, intragranular) in the sintered body, and the degree of densification is insufficient (a relative density of 90 to 95%, for example in Non-Patent Document 2, relative density is 94% when K=Na=0.48, Li=0.04, Nb=0.9 and Ta=0.1, a).
(2) Since the degree of densification is low, there is a possibility that original properties of the material are not utilized.
(3) Since the degree of densification is low, the mechanical strength is insufficient.
(4) There is a research example (for example, Non-Patent Document 1) in which an additive (a sintering aid) such as Cu or Mn is added to raise the degree of densification, but the additive element is dissolved in the (Li, Na, K)(Nb, Ta)O3 type piezoelectric material, and there is the possibility that the original properties are changed.
(5) Since the additive element is added, the composition to be controlled increases.